1. Field of the Invention
The present invention relates to a movable contactor assembly for a circuit breaker, and more particularly, to a movable contactor assembly for a circuit breaker capable of enhancing a current limiting performance by improving an assembly of a movable contactor and a rotation shaft for supporting the movable contactor.
2. Description of the Conventional Art
Generally, a circuit breaker is installed at an electric power distributing board among several electric power systems of a factory and a building. The circuit breaker serves as a switch for supplying or cutting off power to a load side under no load state, and cuts off power supplied to a load side from a power side in order to protect a circuit and components of the load side when a great abnormal current due to a short-circuit or a ground fault flows on a circuit under a load state.
FIG. 1 is a sectional view showing an inner construction of a circuit breaker in accordance with the conventional art, and FIG. 2 is a frontal view of a movable contactor assembly of the circuit breaker in accordance with the conventional art, which shows a closed circuit state, and FIG. 3 is a frontal view of the movable contactor assembly of the circuit breaker in accordance with the conventional art, which shows an opened circuit state.
As shown, a circuit breaker 1 comprises a mold case 10, fixed contactors 20 and 30 installed in the mold case 10 with a predetermined distance, a movable contactor assembly 40 disposed between the fixed contactors 20 and 30, a trip mechanism 50 for tripping the circuit breaker by detecting a large current, a switching mechanism 60 automatically operated by the trip mechanism 50 or manually operated by operating a switching handle 11, for separating a movable contactor 41 from the fixed contactors 20 and 30 thereby cutting off a circuit, and an arc extinguishing mechanism 70 for extinguishing arc gas of a high temperature and a high pressure generated between contacts 41a and 41b of the movable contactor 41 and contacts 21 and 31 of the fixed contacts 20 and 30 at the time of switching a circuit.
The mold case 10 is provided with the above mechanisms therein, and is formed of an insulating material to insulate the mechanisms of phases, and to prevent foreign materials such as dust from being introduced into the mold case 10.
The fixed contactors, that is, a power side fixed contactor 20 and a load side fixed contactor 30 are respectively provided with a contact 21 and a contact 31 at the end thereof. The movable contactor 41 is provided with a contact 41b at both ends thereof.
The movable contactor assembly 40 comprises a movable contactor 41 rotatably positioned between the fixed contactors 20 and 30 for maintaining a closed state or an opened state, a rotation shaft 43 disposed between the fixed contacts 20 and 30 for supporting the movable contactor 41, and a pair of springs 45 and 47 respectively having one ends 45a and 47a fixed to the movable contactor 41 and the other ends 45b and 47b fixed to the rotation shaft 43 for elastically rotating the movable contactor 41 centering around a virtual rotation axis 43a by an electromagnetic repulsive force generated at the contacts 21, 41b, 31 when a large-current flows on a circuit due to a short-circuit or a ground fault. The method for supporting the movable contactor 41 to the rotation shaft 43 centering around the virtual rotation shaft 43a is called as a self centering.
As shown in FIG. 2, a state that the contact 41b of the movable contactor 41 is in contact with the contact 21 and 31 of the fixed contactors 20 and 30 is called as ‘a closed circuit state’. As shown in FIG. 3, a state that the contact 41b of the movable contactor 41 is separated from the contacts 21 and 31 of the fixed contactors 20 and 30 is called as ‘an opened circuit state’. Also, converting the closed circuit state to the opened circuit state is called as ‘separating and opening’.
The movable contactor 41 is supported by the pair of springs 45 and 47 disposed to be symmetrical to each other centering around the virtual rotation axis 43a. 
One ends 45a and 47a of the springs 45 and 47 are fixed to the movable contactor 41, and another ends 45b and 47b thereof are fixed to the rotation shaft 43. Accordingly, as shown in FIG. 2, when a normal current flows on a circuit, the contact 41a and 41b of the movable contactor 41 is in contact with the contacts 21 and 31 of the fixed contactors 20 and 30 thereby to maintain a closed circuit state. Under the state, the springs 45 and 47 provide an elastic force to the movable contactor 41 so that the movable contactor 41 can be maintained in contact with the fixed contactors 20 and 30. Accordingly, an electric current flows from the power side fixed contactor to the load side fixed contactor 30, 20 through the movable contactor 41.
As shown in FIG. 3, when a large current flows on a circuit due to a short-circuit or a ground fault, the movable contactor 41 is separated from the fixed contactors 20 and 30 by an electromagnetic repulsive force between the contacts 41a and 41b of the movable contactor 41 and the contacts 21 and 31 of the fixed contactors 20 and 30 thereby to have a rotation moment. Accordingly, the movable contactor 41 overcomes an elastic force of the springs 45 and 47, and rotates in a clockwise direction thereby to cut off the circuit. An unexplained reference numeral 49 designates a stopper for limiting a rotation range of the movable contactor.
The conventional movable contactor assembly of a circuit breaker has the following problems. When the movable contactor 41 is separated from the fixed contactors 20 and 30, the virtual rotation axis 43a of the movable contactor 41 is not stable, so it cause to generate a fluctuation of the movable contactor 41 in right and left directions and up and down directions. Also, when the movable contactor 41 is separated from the fixed contactors 20 and 30, an elastic restoration force of the springs 45 and 47 increases and thereby the movable contactor 41 becomes in contact with the fixed contactors 20 and 30 again due to the restoration force. That causes a re-contact between the contacts at the time of a short-circuit and a re-separation therebetween by an electromagnetic repulsive force, thereby continuously generating an arc. Accordingly, an instant current limiting characteristic is not obtained and severe damages may be caused to the circuit breaker and the load devices.